Emacs lisp function 'member' takes element and list as an
argument. I.e. the second argument is list, not symbol
referencing the list.
On emacs 23.x the member call always returned nil (thus buggy),
on emacs 22.x the call failed, making it unusable.
(defun notmuch-mua-add-more-hidden-headers ()
"Add some headers to the list that are hidden by default."
(mapc (lambda (header)
- (when (not (member header 'message-hidden-headers))
+ (when (not (member header message-hidden-headers))
(push header message-hidden-headers)))
notmuch-mua-hidden-headers))